The present invention relates to a seat belt retractor with a pretensioner of a type comprising a pipe, a gas generator disposed on one end of the pipe, a piston arranged in the pipe, and balls arranged in the pipe. In particular, the present invention relates to a pretensioner in which the balls are moved via the piston by gas pressure produced by the gas generator and are discharged through an outlet disposed at the other end of the pipe. This type of pretensioner typically includes a pretensioner gear and a gear connected to a spool, which are meshed with each other and rotated by the balls being discharged, thereby pretensioning a seat belt.
A passenger car is normally equipped with seat belt devices for protecting occupants when the car experiences an abrupt deceleration. Such a seat belt device may include a pretensioner which takes up a seat belt around an occupant to restrain the occupant with increased forces when an accident such as a vehicle collision is detected.
There are various types of pretensioners. One known type of pretensioner comprising a pipe, a gas generator disposed on one end of the pipe, a piston arranged in the pipe, and balls arranged in the pipe, in which the balls are moved via the piston by gas pressure produced by the gas generator and are discharged through an outlet disposed at the other end of the pipe, and a pretensioner gear and a gear connected to a spool are meshed with each other and rotated by the balls being discharged, thereby pretensioning a seat belt
In a pretensioner of this type, the pipe should be secured to a pretensioner cover. That is, the pipe should be secured between the pretensioner cover and the pretensioner plate. When the pretensioner is actuated, large force is exerted by gas pressure for moving the balls to pretension the seat belt. A large force is therefore required to retain the pipe. The top of the pipe is retained by the top of the pretensioner cover. It is also required to retain the front end of the pipe where the balls are discharged.
As an example, the pipe may be retained by forming the front end portion of the pipe into a T-shape. The pretensioner cover and the pretensioner plate may be provided with holes for receiving the T-shaped portion. The T-shaped portion may be inserted into the holes, thereby retaining the front end of the pipe.
Though this method can provide a strong retention against vertical forces in the drawing, it is weak against lateral forces (bending stress). That is, the T-shaped front end portion may be easily deformed so as not to exhibit the retaining effect. Accordingly, there is a possibility that during operation, the pretensioner becomes unsteady due to the displacement of the pipe.
The present invention was made taking the aforementioned circumstances into consideration and the object of the invention is to provide a seat belt retractor with a pretensioner of which a front end portion of pipe is securely retained and which can provide steady operation.
The aforementioned object is achieved by a seat belt retractor with a pretensioner of a type comprising a pipe, a gas generator disposed on one end of the pipe, a piston arranged in the pipe, and balls arranged in the pipe, in which the balls are moved via the piston by gas pressure produced by the gas generator and are discharged through an outlet disposed at the other end of the pipe, and a pretensioner gear and a gear connected to a spool are meshed with each other and rotated by the balls being discharged, thereby pretensioning a seat belt, the seat belt retractor being characterized by further comprising a guide block which is fitted into the other end of the pipe to guide the balls to be discharged, and a plate held by a pretensioner cover wherein the pipe and the guide block are secured to the plate by a fastening member.
According to this means, the pipe, the guide block, and the plate are fixed together by the fastening member (for example, a vis) and the plate is held by the pretensioner cover. The portion where the pipe, the guide block, and the plate are fitted and fixed together can provide high rigidity and is thus hardly deformed in every directions, whereby the pipe can be securely retained, thus stabilizing the operation of the pretensioner. When a vise, a rivet, or a spring pin is employed as the fastening member, the fastening member may be hardened or the material for the fastening member may be selected to obtain sufficient strength.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only, and are not restrictive of the invention as claimed.